Chase him around the yard with a turkey leg, he will get tired and eat eventually.
Seriously, about hamburger. the fat content is high as you know - even for a dog, any dog. Tire him out and sprinkle a little less each day, and little less, and wean him off the beef. If he get's too thin the resume the previous diet. You dog is smart, mine got it but good yesterday, when she ran the other way, I told her for that, I will trade her in for a Yorkie !